1. Field of the Invention
The invention relates generally to systems and methods for performing a reaction in a small volume without incurring an undesirable loss of the reaction volume due to evaporation, and more specifically to systems and methods for performing reactions involving polymers, particularly biopolymers, in a reaction volume of a few microliters or less in an unsealed environment.
2. Background Information
Technological advances have allowed an examination of previously undiscernible phenomena. Such advances are particularly notable in the biological sciences, where the chemical and physical structures of many biopolymers have been described, and where such biopolymers, including DNA and proteins, routinely are synthesized and sequenced.
Although methods such as nucleic acid sequencing and synthesis have contributed to understanding the structure and function of biological molecules and their relationships to disease, the limitations of such methods are apparent. For example, it generally is agreed that knowledge of the entire sequence of the human genome would provide valuable insight into the prevention and treatment of disease. The human genome, however, contains over one billion nucleotides and a huge expenditure of labor and money would be required to sequence the entire human genome. Furthermore, using currently available methods, many years will be required to see the project to completion.
Similarly, it is a goal of most clinical researchers to develop rapid and simple tests for determining whether an individual has a disease or predisposition to a disease. In many cases, the signs and symptoms of many genetic diseases do not become apparent until an individual reaches a certain age or stage of development. Knowledge that an individual has a predisposition to a genetic disease can allow the clinician to take prophylactic measures to minimize or delay onset of the disease. Ideally, all individuals would be screened for potential genetically determined diseases, including screening a large number of genes in each individual. Unfortunately, such routine screening currently is not feasible because the assays are time consuming and the reagents for performing such assays are expensive and limited in availability.
In an effort to reduce the time and cost for analyzing biopolymers, including genes and proteins, processes are being developed to automate the analytic procedures. Automation provides a means for performing repetitive processes almost continually, except for periodic breaks for equipment maintenance, and allows researchers and technical staff to devote more time to other endeavors, including interpreting the results produced by the automated assays and troubleshooting problems that may arise. Automation of repetitive processes also provides the advantage that the likelihood of errors occurring, for example, due to fatigue or distraction is reduced and, therefore, more accurate results can be obtained.
The application of nanotechnology to the biological sciences promises to provide the next breakthroughs relating, for example, to the analysis, synthesis and utilization of biopolymers. Nanotechnology, which provides processes and apparatuses for performing procedures on a very small scale, has been developed by the semiconductor industry in order to produce smaller and smaller microchips, and to allow placement of a continually increasing number of instructions on a microchip.
Efforts are in progress to apply nanotechnology to chemical and biological procedures, thereby providing a means to perform assays in very small volumes, generally a few hundred nanoliters or less. Application of nanotechnology to biological assays can be particularly valuable because a critical limitation of many biological assays is the amount of biological material available for analysis. By performing such assays in nanoliter volumes or smaller, the effective concentration of a biopolymer in a biological reaction is increased, thereby providing the necessary kinetics for a biological reaction to proceed. In addition, the ability to perform biological assays in nanoliter volumes can provide a significant cost savings because much smaller amounts of reagents, which can be very expensive, can be utilized in the reactions.
The application of nanotechnology to biological assays has been hindered, in part, by the difficulty in manipulating and maintaining such small volumes. Many biological assays, for example, are performed in aqueous conditions, using water as a solvent, and at elevated temperatures, generally at least 37.degree. C., which is human body temperature. Water, like many liquid solvents, is susceptible to evaporation and, therefore, as the time or temperature of a reaction increases, the loss of water due to evaporation increases and the volume of the reaction decreases. As a result of evaporation, the effective concentration of reagents in the reaction increases, thereby changing the conditions of the reaction. Since most biological assays are quite sensitive to reaction conditions, loss of water or other solvent from a reaction can result in an assay that produces spurious results. Any loss of a solvent such as water is particularly deleterious when the reaction contains only a few hundred nanoliters or less of the liquid, since the reaction quickly can evaporate to dryness.
Various methods have been used to minimize the loss of solvent in a reaction due to evaporation in biochemical assays. For example, reaction mixtures can be drawn into glass capillary tubes, which then are sealed at both ends for the reaction. Small volume glass capillary tubes can be expensive, and the use of such tubes requires additional steps, including sealing and unsealing the tube, the latter which can produce glass shards.
In many cases, reaction mixtures are performed in a microcentrifuge tube or other open chamber, and evaporation is minimized by overlaying the reaction mixture with wax, mineral oil, or other nonvolatile compound during the reaction. Such a method, again, requires additional steps, including removing the sealing material following the reaction. In order to remove all or most of the sealing material, which can otherwise contaminate the sample and hinder further analysis, some loss of the sample being assayed inevitably occurs. Since most biological samples are limited to begin with, any loss of sample can preclude an interpretation of the results of the assay. In general, any additional manipulations of a sample will incur extra cost, either in terms of time or money, and loss or contamination of the sample.
More recently, biological reactions have been performed on microchips, which conveniently can be adapted to automated processes. Such microchips have been designed having a system including, for example, chambers, which hold the reactants, and channels, which connect the chambers and in which the reactants can be mixed and a reaction performed. Since the channels, in which the reaction occurs, provide a sealed or closed environment, there is little or no evaporative loss of the reaction volume. Thus far, however, the technology for preparing such a device allows for the placement of only one or few of such closed systems on a single microchip and, therefore, the number of reactions that can be performed at one time on a single chip is limited. Thus, a need exists for systems useful for performing reactions in a volume of a few microliters or less in an unsealed environment. Therefore it is an object here to provide systems and methods that satisfy this need and also provide additional advantages.